The invention relates to a transducer, in particular suitable for hearing aids, comprising a coil having a first air gap, a magnetic member having a second air gap, and an armature, the first and the second air gaps being in line, and the armature comprising an armature leg extending through both air gaps.
Such transducers are known per se. The above armature leg is connected therein with a diaphragm. Vibrations of the diaphragm are transmitted to the armature leg, and the vibrating armature leg causes an electric alternating current in the coil. Conversely, an alternating current supplied to the coil causes a vibration of the armature leg, which is transmitted to the diaphragm.
With the vibrations of the above armature leg occurring under normal conditions the displacements thereof are relatively small. In extreme cases, however, the armature leg can touch the magnet.
Transducers of the above type have the problem that when a shock or impact load is exerted on the transducer, such as, e.g., when the transducer falls, the armature leg bends so far that plastic deformations can occur in the armature leg, which is undesirable.
A transducer of the above type is described, e.g., in the international patent application WO 94/10817. In this publication the above shock problem is already recognized, and the publication describes different limiting means for increasing the shock resistance of a transducer. These means are based on the limitation of the freedom of movement of the above armature leg in a central position thereof.
In one embodiment these limiting means are a projection formed as a deformation at the armature leg.
In another embodiment these limiting means are a separate stop member functioning as a bumper, which may be fitted to the armature leg.
In yet another embodiment these limiting means are a separate spacer with a limited air gap, which is arranged between the coil and the magnet.
In yet another embodiment the publication proposes to give the interior of the coil body a specific form.
All these proposals, however, have the disadvantage that it is not possible to make use of standard parts and/or that additional parts must be added. This increases the expenses associated with such a transducer.
Another disadvantage of the above proposals is that it is not possible to adjust the protective means. In general, the coil is wound on a coil body formed as an injection molded product and therefore has a certain tolerance. When the interior of a coil is used as a stop in the manner as proposed in the above publication, a rather large spreading of the shock resistance of the individual transducers is obtained, which spreading cannot be reduced by an adjusting procedure.
Another disadvantage of the above proposals is the fact that it is desirable for a proper and reliable operation of the transducer that the armature leg is symmetrically positioned in the magnet housing and that the protective means have a symmetrical effect in both directions of vibration of the armature leg. This implies that the parts proposed by the above publication must be produced with a rather high accuracy.